lecture 16 Flashcards
what is prevalence
The proportion of a population who have the disease at a point in time
whats prevalence equation
Number of people with the disease at a given point in time/
Total number of people in the population at that point in time
how do we report prevalence
The prevalence of outcome in POPULATION at TIME POINT was VALUE
whats the difference between incidence rate and incidence proportion
Key difference is what we use as the denominator
define incidence
The occurrence of new cases of an outcome in a population during a specific period of follow-up
definition of incidence proportion
The proportion of an outcome-free population that develops the outcome of interest in a specified time period
whats the calculation of incidence proportion
Number of people at risk of developing the disease at the start of the period
why might someone not be at risk for a disease
They already have the condition
The condition is something that they cannot develop
limitations of incidence proportion
- Assumes a ‘closed’ population
(does not account for people coming or going) - Highly dependent on the time period
(longer time period = higher incidence proportion)
define incidence rate
The rate at which new cases of the outcome of
interest occur in a population
whats incidence rate calculation
Number of person-years at risk of developing the disease
whats person years
Sum of everyone in the population’s time at risk of becoming a case
why may someone not be at risk in incidence rate
*They become a case
* They are lost to follow-up
(e.g. die, move away, no longer take part)
* Follow-up time ends
limitations of incidence rate
Person-time not available
Complex to calculate
what is prevalence affected by
time and incidence
what do we do when populations we compare vary by age structure
age standardisation
what two things make us need to age standardise
Age structures differ
AND
Disease risk varies by age
why do we report prevalence
we can determine the burden of disease and see where resources need to be allocated
whats some limitations of prevalence
difficult to assess development of a disease
it is influenced by duration of a disease
how do we report incidence proportion
the incidence proportion of Outcome in Population in the Specified time period was Value
why might we use incidence rate
to meausre how quickly new cases of the outcome are developing in the population
